[PATCH bpf-next v2 1/3] bpftool: Skip non-autoload programs when generating light skeletons

[PATCH bpf-next v2 1/3] bpftool: Skip non-autoload programs when generating light skeletons

[Thiébaud Weksteen]

When generating a light skeleton (bpftool gen skeleton -L),
bpf_object__load() skips loading programs marked as non-autoload (e.g.
SEC("?...")), so the generated loader program only records and populates
file descriptors for autoloaded programs.

Previously, bpftool emitted struct bpf_prog_desc fields, link fields,
and attach/detach/destroy functions for all programs in the BPF object,
causing the loader program to store subsequent program FDs into
incorrect skeleton struct fields when non-autoload programs were
present.

Furthermore, bpf_object__load() can update a program's autoload status
during preparation (e.g. for struct_ops programs when resolving kernel
BTF members or adjusting autoload based on map autocreate settings).
Move bpf_object__gen_loader() and bpf_object__load() out of gen_trace()
into do_skeleton() before counting programs and emitting struct fields so
that struct field declarations and attach/detach/destroy functions all
observe the final post-load autoload state.

Skip programs with !bpf_program__autoload(prog) when counting programs
and generating progs/links struct fields as well as attach, detach, and
destroy functions for light skeletons.

Fixes: d510296d331a ("bpftool: Use syscall/loader program in "prog load" and "gen skeleton" command.")
Signed-off-by: Thiébaud Weksteen <tweek@google.com>
---
Changes since v1:
- Move bpf_object__gen_loader() and bpf_object__load() out of gen_trace()

 .../bpf/bpftool/Documentation/bpftool-gen.rst |  4 +-
 tools/bpf/bpftool/gen.c                       | 64 ++++++++++++-------
 2 files changed, 44 insertions(+), 24 deletions(-)

diff --git a/tools/bpf/bpftool/Documentation/bpftool-gen.rst b/tools/bpf/bpftool/Documentation/bpftool-gen.rst
index d0a36f442db7..1cdecf3e4fa5 100644
--- a/tools/bpf/bpftool/Documentation/bpftool-gen.rst
+++ b/tools/bpf/bpftool/Documentation/bpftool-gen.rst
@@ -184,7 +184,9 @@ OPTIONS
 -L, --use-loader
     For skeletons, generate a "light" skeleton (also known as "loader"
     skeleton). A light skeleton contains a loader eBPF program. It does not use
-    the majority of the libbpf infrastructure, and does not need libelf.
+    the majority of the libbpf infrastructure, and does not need libelf. BPF
+    programs marked as non-autoload (e.g., via **SEC("?...")**) are skipped and
+    not included in the generated skeleton.
 
 -S, --sign
     For skeletons, generate a signed skeleton. This option must be used with
diff --git a/tools/bpf/bpftool/gen.c b/tools/bpf/bpftool/gen.c
index a50540ef6521..e9a1a018f270 100644
--- a/tools/bpf/bpftool/gen.c
+++ b/tools/bpf/bpftool/gen.c
@@ -583,6 +583,9 @@ static void codegen_attach_detach(struct bpf_object *obj, const char *obj_name)
 	bpf_object__for_each_program(prog, obj) {
 		const char *tp_name;
 
+		if (!bpf_program__autoload(prog))
+			continue;
+
 		codegen("\
 			\n\
 			\n\
@@ -629,6 +632,8 @@ static void codegen_attach_detach(struct bpf_object *obj, const char *obj_name)
 		", obj_name);
 
 	bpf_object__for_each_program(prog, obj) {
+		if (!bpf_program__autoload(prog))
+			continue;
 		codegen("\
 			\n\
 				ret = ret < 0 ? ret : %1$s__%2$s__attach(skel);   \n\
@@ -646,6 +651,8 @@ static void codegen_attach_detach(struct bpf_object *obj, const char *obj_name)
 		", obj_name);
 
 	bpf_object__for_each_program(prog, obj) {
+		if (!bpf_program__autoload(prog))
+			continue;
 		codegen("\
 			\n\
 				skel_closenz(skel->links.%1$s_fd);	    \n\
@@ -676,6 +683,8 @@ static void codegen_destroy(struct bpf_object *obj, const char *obj_name)
 		obj_name);
 
 	bpf_object__for_each_program(prog, obj) {
+		if (!bpf_program__autoload(prog))
+			continue;
 		codegen("\
 			\n\
 				skel_closenz(skel->progs.%1$s.prog_fd);	    \n\
@@ -701,9 +710,9 @@ static void codegen_destroy(struct bpf_object *obj, const char *obj_name)
 		obj_name);
 }
 
-static int gen_trace(struct bpf_object *obj, const char *obj_name, const char *header_guard)
+static int gen_trace(struct bpf_object *obj, const char *obj_name, const char *header_guard,
+		     const struct gen_loader_opts *opts)
 {
-	DECLARE_LIBBPF_OPTS(gen_loader_opts, opts);
 	struct bpf_load_and_run_opts sopts = {};
 	char sig_buf[MAX_SIG_SIZE];
 	__u8 prog_sha[SHA256_DIGEST_LENGTH];
@@ -712,19 +721,6 @@ static int gen_trace(struct bpf_object *obj, const char *obj_name, const char *h
 	char ident[256];
 	int err = 0;
 
-	if (sign_progs)
-		opts.gen_hash = true;
-
-	err = bpf_object__gen_loader(obj, &opts);
-	if (err)
-		return err;
-
-	err = bpf_object__load(obj);
-	if (err) {
-		p_err("failed to load object file");
-		goto out;
-	}
-
 	/* If there was no error during load then gen_loader_opts
 	 * are populated with the loader program.
 	 */
@@ -752,7 +748,7 @@ static int gen_trace(struct bpf_object *obj, const char *obj_name, const char *h
 				goto cleanup;				    \n\
 			skel->ctx.sz = (char *)&skel->links - (char *)skel; \n\
 		",
-		obj_name, opts.data_sz);
+		obj_name, opts->data_sz);
 	bpf_object__for_each_map(map, obj) {
 		const void *mmap_data = NULL;
 		size_t mmap_size = 0;
@@ -795,22 +791,22 @@ static int gen_trace(struct bpf_object *obj, const char *obj_name, const char *h
 			static const char opts_data[] __attribute__((__aligned__(8))) = \"\\\n\
 		",
 		obj_name);
-	print_hex(opts.data, opts.data_sz);
+	print_hex(opts->data, opts->data_sz);
 	codegen("\
 		\n\
 		\";							    \n\
 			static const char opts_insn[] __attribute__((__aligned__(8))) = \"\\\n\
 		");
-	print_hex(opts.insns, opts.insns_sz);
+	print_hex(opts->insns, opts->insns_sz);
 	codegen("\
 		\n\
 		\";\n");
 
 	if (sign_progs) {
-		sopts.insns = opts.insns;
-		sopts.insns_sz = opts.insns_sz;
-		sopts.data = opts.data;
-		sopts.data_sz = opts.data_sz;
+		sopts.insns = opts->insns;
+		sopts.insns_sz = opts->insns_sz;
+		sopts.data = opts->data;
+		sopts.data_sz = opts->data_sz;
 		sopts.excl_prog_hash = prog_sha;
 		sopts.excl_prog_hash_sz = sizeof(prog_sha);
 		sopts.signature = sig_buf;
@@ -1250,6 +1246,7 @@ static int do_skeleton(int argc, char **argv)
 	char header_guard[MAX_OBJ_NAME_LEN + sizeof("__SKEL_H__")];
 	size_t map_cnt = 0, prog_cnt = 0, attach_map_cnt = 0, file_sz, mmap_sz;
 	DECLARE_LIBBPF_OPTS(bpf_object_open_opts, opts);
+	DECLARE_LIBBPF_OPTS(gen_loader_opts, gen_opts);
 	char obj_name[MAX_OBJ_NAME_LEN] = "", *obj_data;
 	struct bpf_object *obj = NULL;
 	const char *file;
@@ -1326,6 +1323,21 @@ static int do_skeleton(int argc, char **argv)
 		goto out_obj;
 	}
 
+	if (use_loader) {
+		if (sign_progs)
+			gen_opts.gen_hash = true;
+
+		err = bpf_object__gen_loader(obj, &gen_opts);
+		if (err)
+			goto out;
+
+		err = bpf_object__load(obj);
+		if (err) {
+			p_err("failed to load object file");
+			goto out;
+		}
+	}
+
 	bpf_object__for_each_map(map, obj) {
 		if (!get_map_ident(map, ident, sizeof(ident))) {
 			p_err("ignoring unrecognized internal map '%s'...",
@@ -1339,6 +1351,8 @@ static int do_skeleton(int argc, char **argv)
 		map_cnt++;
 	}
 	bpf_object__for_each_program(prog, obj) {
+		if (use_loader && !bpf_program__autoload(prog))
+			continue;
 		prog_cnt++;
 	}
 
@@ -1402,6 +1416,8 @@ static int do_skeleton(int argc, char **argv)
 	if (prog_cnt) {
 		printf("\tstruct {\n");
 		bpf_object__for_each_program(prog, obj) {
+			if (use_loader && !bpf_program__autoload(prog))
+				continue;
 			if (use_loader)
 				printf("\t\tstruct bpf_prog_desc %s;\n",
 				       bpf_program__name(prog));
@@ -1415,6 +1431,8 @@ static int do_skeleton(int argc, char **argv)
 	if (prog_cnt + attach_map_cnt) {
 		printf("\tstruct {\n");
 		bpf_object__for_each_program(prog, obj) {
+			if (use_loader && !bpf_program__autoload(prog))
+				continue;
 			if (use_loader)
 				printf("\t\tint %s_fd;\n",
 				       bpf_program__name(prog));
@@ -1451,7 +1469,7 @@ static int do_skeleton(int argc, char **argv)
 			goto out;
 	}
 	if (use_loader) {
-		err = gen_trace(obj, obj_name, header_guard);
+		err = gen_trace(obj, obj_name, header_guard, &gen_opts);
 		goto out;
 	}
 
-- 
2.55.0.979.g7e5102b832-goog

[PATCH bpf-next v2 2/3] bpftool: Compute light skeleton ctx.sz without relying on links

[Thiébaud Weksteen]

When generating a light skeleton, gen_trace() unconditionally sets
skel->ctx.sz using (char *)&skel->links - (char *)skel. However, if a
BPF object has no programs and no struct_ops maps (prog_cnt +
attach_map_cnt == 0), do_skeleton() omits the links struct, causing the
generated skeleton header to fail compilation.

Compute skel->ctx.sz from the end of progs (if prog_cnt > 0), maps (if
map_cnt > 0), or ctx instead of relying on skel->links. Also remove the
unused opts.data_sz argument passed to codegen().

Fixes: d510296d331a ("bpftool: Use syscall/loader program in "prog load" and "gen skeleton" command.")
Signed-off-by: Thiébaud Weksteen <tweek@google.com>
---
 tools/bpf/bpftool/gen.c | 15 +++++++++++----
 1 file changed, 11 insertions(+), 4 deletions(-)

diff --git a/tools/bpf/bpftool/gen.c b/tools/bpf/bpftool/gen.c
index e9a1a018f270..4a93c392857a 100644
--- a/tools/bpf/bpftool/gen.c
+++ b/tools/bpf/bpftool/gen.c
@@ -711,7 +711,7 @@ static void codegen_destroy(struct bpf_object *obj, const char *obj_name)
 }
 
 static int gen_trace(struct bpf_object *obj, const char *obj_name, const char *header_guard,
-		     const struct gen_loader_opts *opts)
+		     const struct gen_loader_opts *opts, size_t prog_cnt, size_t map_cnt)
 {
 	struct bpf_load_and_run_opts sopts = {};
 	char sig_buf[MAX_SIG_SIZE];
@@ -746,9 +746,16 @@ static int gen_trace(struct bpf_object *obj, const char *obj_name, const char *h
 			skel = (struct %1$s *)skel_alloc(sizeof(*skel));    \n\
 			if (!skel)					    \n\
 				goto cleanup;				    \n\
-			skel->ctx.sz = (char *)&skel->links - (char *)skel; \n\
 		",
-		obj_name, opts->data_sz);
+		obj_name);
+	if (prog_cnt)
+		printf("\tskel->ctx.sz = (char *)&skel->progs - (char *)skel\n"
+		       "\t\t       + sizeof(skel->progs);\n");
+	else if (map_cnt)
+		printf("\tskel->ctx.sz = (char *)&skel->maps - (char *)skel\n"
+		       "\t\t       + sizeof(skel->maps);\n");
+	else
+		printf("\tskel->ctx.sz = sizeof(skel->ctx);\n");
 	bpf_object__for_each_map(map, obj) {
 		const void *mmap_data = NULL;
 		size_t mmap_size = 0;
@@ -1469,7 +1476,7 @@ static int do_skeleton(int argc, char **argv)
 			goto out;
 	}
 	if (use_loader) {
-		err = gen_trace(obj, obj_name, header_guard, &gen_opts);
+		err = gen_trace(obj, obj_name, header_guard, &gen_opts, prog_cnt, map_cnt);
 		goto out;
 	}
 
-- 
2.55.0.979.g7e5102b832-goog

[PATCH bpf-next v2 3/3] selftests/bpf: Verify program FD after non-autoload programs in lskel

[Thiébaud Weksteen]

In test_global_percpu_data.c, dump_percpu_data is defined after two
non-autoload SEC("?kprobe") programs (verifier_strncmp and
verifier_snprintf). Verify in test_global_percpu_data_lskel() that
lskel->progs.dump_percpu_data.prog_fd is properly populated (> 0) when
loaded via the light skeleton.

Signed-off-by: Thiébaud Weksteen <tweek@google.com>
---
No changes since v1.

 tools/testing/selftests/bpf/prog_tests/global_data_init.c | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/tools/testing/selftests/bpf/prog_tests/global_data_init.c b/tools/testing/selftests/bpf/prog_tests/global_data_init.c
index 7c539cbcf3a1..ebda60200b71 100644
--- a/tools/testing/selftests/bpf/prog_tests/global_data_init.c
+++ b/tools/testing/selftests/bpf/prog_tests/global_data_init.c
@@ -214,6 +214,8 @@ static void test_global_percpu_data_lskel(void)
 	lskel = test_global_percpu_data_lskel__open_and_load();
 	if (!ASSERT_OK_PTR(lskel, "test_global_percpu_data_lskel__open_and_load"))
 		goto out;
+	if (!ASSERT_GT(lskel->progs.dump_percpu_data.prog_fd, 0, "dump_percpu_data.prog_fd"))
+		goto out;
 
 	map_fd = lskel->maps.percpu.map_fd;
 	prog_fd = lskel->progs.update_percpu_data.prog_fd;
-- 
2.55.0.979.g7e5102b832-goog

Re: [PATCH bpf-next v2 1/3] bpftool: Skip non-autoload programs when generating light skeletons

[bot+bpf-ci]

[-- Attachment #1: Type: text/plain, Size: 1824 bytes --]

> diff --git a/tools/bpf/bpftool/gen.c b/tools/bpf/bpftool/gen.c
> index a50540ef6521..e9a1a018f270 100644
> --- a/tools/bpf/bpftool/gen.c
> +++ b/tools/bpf/bpftool/gen.c

[ ... ]

> @@ -701,9 +710,9 @@ static void codegen_destroy(struct bpf_object *obj, const char *obj_name)
>  		obj_name);
>  }
>
> -static int gen_trace(struct bpf_object *obj, const char *obj_name, const char *header_guard)
> +static int gen_trace(struct bpf_object *obj, const char *obj_name, const char *header_guard,
> +		     const struct gen_loader_opts *opts)
>  {
> -	DECLARE_LIBBPF_OPTS(gen_loader_opts, opts);
>  	struct bpf_load_and_run_opts sopts = {};
>  	char sig_buf[MAX_SIG_SIZE];
>  	__u8 prog_sha[SHA256_DIGEST_LENGTH];
> @@ -712,19 +721,6 @@ static int gen_trace(struct bpf_object *obj, const char *obj_name, const char *h
>  	char ident[256];
>  	int err = 0;
>
> -	if (sign_progs)
> -		opts.gen_hash = true;
> -
> -	err = bpf_object__gen_loader(obj, &opts);
> -	if (err)
> -		return err;
> -
> -	err = bpf_object__load(obj);
> -	if (err) {
> -		p_err("failed to load object file");
> -		goto out;
> -	}
> -
>  	/* If there was no error during load then gen_loader_opts
>  	 * are populated with the loader program.
>  	 */

This isn't a bug, but now that the bpf_object__load() call moved to
do_skeleton(), would this comment be clearer next to the new call site, or
reworded as a precondition on the opts parameter? The comment currently sits
at the top of gen_trace() followed immediately by another unrelated comment,
and a reader has to look at the caller to find the load it refers to.


---
AI reviewed your patch. Please fix the bug or email reply why it's not a bug.
See: https://github.com/kernel-patches/vmtest/blob/master/ci/claude/README.md

CI run summary: https://github.com/kernel-patches/bpf/actions/runs/34311359322

Re: [PATCH bpf-next v2 3/3] selftests/bpf: Verify program FD after non-autoload programs in lskel

[Leon Hwang]

On 9/9/26 12:24, Thiébaud Weksteen wrote:
> In test_global_percpu_data.c, dump_percpu_data is defined after two
> non-autoload SEC("?kprobe") programs (verifier_strncmp and
> verifier_snprintf). Verify in test_global_percpu_data_lskel() that
> lskel->progs.dump_percpu_data.prog_fd is properly populated (> 0) when
> loaded via the light skeleton.
> 
> Signed-off-by: Thiébaud Weksteen <tweek@google.com>
> ---
> No changes since v1.

The Fixes tags of v1 are dropped.

> 
>  tools/testing/selftests/bpf/prog_tests/global_data_init.c | 2 ++
>  1 file changed, 2 insertions(+)
> 
> diff --git a/tools/testing/selftests/bpf/prog_tests/global_data_init.c b/tools/testing/selftests/bpf/prog_tests/global_data_init.c
> index 7c539cbcf3a1..ebda60200b71 100644
> --- a/tools/testing/selftests/bpf/prog_tests/global_data_init.c
> +++ b/tools/testing/selftests/bpf/prog_tests/global_data_init.c
> @@ -214,6 +214,8 @@ static void test_global_percpu_data_lskel(void)
>  	lskel = test_global_percpu_data_lskel__open_and_load();
>  	if (!ASSERT_OK_PTR(lskel, "test_global_percpu_data_lskel__open_and_load"))
>  		goto out;
> +	if (!ASSERT_GT(lskel->progs.dump_percpu_data.prog_fd, 0, "dump_percpu_data.prog_fd"))
> +		goto out;

When the light skeleton does not skip the non-autoload progs,
lskel->progs.dump_percpu_data.prog_fd is 0, actually.

But, theoretically, this ASSERT_GT() is not good enough to prove the FD
is the correct FD of dump_percpu_data prog.

How about running the iter subtest against the lskel? Factor out
test_global_percpu_data_iter_fd() helper first. Then, add an iter
subtest using lskel.
When factoring out test_global_percpu_data_iter_fd() helper, pls change
'do { } while (0);' to '{ /* no-op */ }' btw.

Thanks,
Leon